Overhead projectors are widely used for the presentation of educational and commerical material. Such projectors comprise a transparent glass stage, a light source below the stage and a reflector above the stage which projects images received from the stage onto a screen. The images to be projected are usually printed or drawn on transparent plastic sheets, referred to as transparencies or slides. The transparent glass stage on which the transparencies are placed is usually a square 10".times.10" or 11".times.11" upon which a transparency, usually 81/2.times.11, can be positioned and projected either vertically or horizontally. So that the stage can be as versatile as possible it is usually not provided with any registry means which are used to insure proper positioning of the transparencies on the stage or any means of framing the transparency to avoid the projection of extraneous material or light.
In the past, a number of suppliers have provided their transparencies in the form of books or packs with registry means and/or framing means. However, because of the added cost of such books or packs the suppliers of overhead transparencies have increasingly taken to simply supplying the transparencies in a conventional three-ring binder without any registry means or framing means. As a result, if the user of an overhead projector wants to insure that the transparency is properly aligned or two or more overlaid transparencies are in register, he has to devise his own registry means for keeping slides properly aligned or framing means so that extraneous light or material is not projected. Some users have used masking tape to secure the transparency in place, but obviously each time a transparency is replaced, the tape has to be lifted and reapplied. To prevent the extraneous material light from coming through, some users have used wide tape to both secure and frame the transparencies or put the transparencies into cardboard frames. However, the latter is a relatively expensive process when a large number of transparencies are involved.
Obviously, it would be advantageous to have a simple inexpensive device that would permit the user to both properly align transparencies supplied in three-ring binders on the glass stage of a projector and to frame the transparencies, if desired.